Mac OS X 10.6.8 Brings TRIM Support for SSDs

“One item of interest regarding last week’s Mac OS X 10.6.8 update reveals that Apple has enabled TRIM support retroactively for solid state hard drives shipped in Apple-produced configurations. TRIM is a feature that allows solid state drives (SSDs) to automatically handle garbage collection, cleaning up unused blocks of data and preparing them for rewriting, thereby preventing slowdowns that would otherwise occur over time as garbage data accumulates.”

There are some relatively minor benefits to TRIM support, for relatively empty drives. But once your drive fills past a certain point, you get diminishing returns. Any decent GC algorithm, with an appropriate level of overprovisioning, will make the drive perform well regardless of TRIM support.

Don’t buy a drive whose firmware depends on TRIM for good performance. Instead, evaluate drives based on their performance when the disk is nearly full. This is especially important for things like database workloads where TRIM is useless, because you keep overwriting parts of one big file. You also can’t use TRIM with RAID, otherwise your parity will be wrong for trimmed blocks.

I’m not saying that Apple shouldn’t support it. If it’s there and it works, then great. You’ll get marginally better write performance on drives that aren’t very full.